1. Field of the Invention:
The present invention relates to a vibration sensor, and more particularly to a vibration sensor for detecting vibration at a desired frequency.
2. Description of the Relevant Art:
Where the frequency of vibration of an automotive engine mount or suspension is detected for use in various control processes, it has been customary to employ a vibration sensor comprising a weight and a piezoelectric device for detecting such vibration. A fluctuating voltage produced by the vibration sensor is passed through a filter circuit, which generates an electric signal in a certain frequency range. The electric signal is applied to a control circuit for operating an actuator or actuators.
Such a vibration sensor is utilized as a road condition sensor in Japanese Laid-Open Patent Publication No. 60-151110 published Aug. 9, 1985. The road condition sensor is mounted on an automobile suspension and converts vibration applied by a road to the automobile into an electric signal commensurate with the vibration frequency. The road condition sensor however tends to generate electric signals of vibration frequencies outside of a certain frequency range that is desired for operating various actuators on the automobile. Therefore, various filter circuits have been needed, in addition to the sensor itself, for extracting an electric signal in the desired frequency range for operating the actuators, from the electric signals generated by the sensor. There has been a demand for simplification of vibration detecting devices and a reduction in the number of parts required of the vibration detecting devices.